He was useful because he had been instructed; and what he knew was this — that should the water in that transparent thing disappear, the evil spirit inside the boiler would get angry through the greatness of his thirst, and take a terrible vengeance. So he sweated and fired up and watched the glass fearfully (with an impromptu charm, made of rags, tied to his arm, and a piece of polished bone, as big as a watch, stuck flatways through his lower lip), while the wooded banks slipped past us slowly, the short noise was left behind, the interminable miles of silence — and we crept on, towards Kurtz.

But the snags were thick, the water was treacherous and shallow, the boiler seemed indeed to have a sulky devil in it, and thus neither that fireman nor I had any time to peer into our creepy thoughts.